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Transcript of Presentation sampling
EDU 702 :Research MethodologySampling
Adibah Halilah bt Abdul Mutalib
Topic areas:
Definition
• Population• Sample
Identify & Contrast
• Target and Accessible population• Random Sampling and Non-Random
Random Sampling
• Types of Random Sampling.• How to select a random sample.
Problem : Relationship between stress levels and smoking among university students
Population of all university students in Malaysia = 12,000
Population of university students in UITM = 4,000
10% Populations of UITM first year male students = 140
Research question : You would like to know the number of cigarettes the average university students smokes
Definition of a Sample
Sample•A small group of people studied to collect information to draw conclusion about the larger group
Sampling
•Process of selecting the people (individuals) to be observed ( studied)
Example of sample within a population
Sample: information obtained
Population: results of studies applied here
700
70
Questions: Can a Sample & Population have the same groups of people?
Smokers at UniversityAll smokers
Population – Smokers at University
Sample – Year 1 university students who are smokers
Discussion: How to select Sample?
Effects of eating “Nasi Lemak” for breakfast on young students.
Teachers view about teaching Math and Science in Bahasa Malaysia.
Students addiction to computer games and poor grades.
How to define the population
Stage 1: Define the population• W
ho can you administer the results to?
• Any size
• Need to have at least one characteristic different from other population
Stage 2 : Identify “Who” or “What”• E
ducator
• Object
TARGET vs. ACCESSIBLE POPULATION
•Ideal group/actual group researchers like to generalize•Rarely available
TARGET
•Those who researchers are able to generalize•Actual choice
ACCESSIBLE
Advantages of defining & narrowing population
Money Time Effort
Random vs. Non-random-Sampling
Random Non-Sampling (Purposive)
All have equal and independent chance
Chosen based on a criteria
Selects a representative of population
No equal chance
Should be large and random Some have no chance at all
No bias Some types show biasness
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Random Sampling Methods(A) Simple Random Sampling
(B) Stratified Random Sampling
(C) Cluster Random Sampling
(D) Two-stage Random Sampling
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(A) Simple Random Sampling ( 1 of 2)
• Each individual has equal and independent chance of selection
• The larger the sample, the more it represents the population
• Any differences is not due to biasness
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Simple Random Sampling (2 of 2)
• Method of finding individuals :
Use a table of random numbers ( statistic book)
Choose any number on the column
Read the numbers to select your sample
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Using the Table of Random Numbers
• Step 1: Select column of numbers• Step 2: Choose any number on the column• Step 3: Read the first 4 digits ( if you have
population of 4 digits)• Step 4: Pick out numbers and write them
down.
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Exercise: Select the first 30 numbers for a population of 300.
Column 1 Column 2 Column 3 Column 4
099922 231100 182203 012030122331 334444 092010 231102644632 088765 001220 120301162311 755664 005440 909201234577 112344 194020 718291344666 412346 230440 503813092303 080902 210490 120311009330 006102 530209 301020230420 003233 409201 015663
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Answer:
• Looking at column 1:– Selected individuals are :
• 099 • 122• 644• 162• 234• 344• 092• 009• 230
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(B) Stratified Random Sampling
• Certain ‘strata’ selected• Sample in same proportion as they exist in the
population• Advantages: Increases likelihood of
representativeness
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Calculating Stratified Random Sampling
• Step 1: Identify the target ( accessible) population
• Step 2: Select the ratio of their relationship• Step 3: Determine the % of target population
used as sample• Step 4: Calculate the % sample for each strata• Step 5: Use Table of random numbers to find
the individuals in the respective strata
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Select gender individuals as they exist in the population ( 365)
Female • 60 %• 60 % of 365 = 219
Male• 40%• 40 % of 365 = 146
Therefore, Female : Male 60 : 40 219 : 146
Now, select 40 % of each strata as you representative… Female : Male 88 : 58
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(C ) Cluster Random Sampling
• Ideal to include certain groups/ cluster • However at times it is not possible to select
individual due to • Time• Effort
• Select individuals based on ( not individuals)• Groups• Clusters• Subjects
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All Year 6 students in Selangor
1
98
1110
1312
7
6
1
5
43
2
Selected schools chosen as clusters
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Cluster random sampling…
Advantages
Disadvantages
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Common mistake made with Cluster random sampling.
• Randomly selecting only one cluster as a sample and choosing to interview/ survey all
• Cluster must be randomly selected not individuals
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(D) Two-stage Random Sampling
• Combination of Cluster random sampling and individual random sampling– First select clusters randomly– Then select students randomly from the clusters.
FD
ABPO
KJ
XT
NH
RS
XT
PO
RS
P, T, S
27
Thank you…